10:03 p.m.
I'm still working my way through the filters before this series will
be complete, but this is enough of a start to at least get some
feedback on the idea of implementing another NBD protocol extension.
Eric Blake (9):
server: Internal hooks for implementing NBD_CMD_CACHE
plugins: Add .cache callback
file, split: Implement .cache with posix_fadvise
nbd: Implement NBD_CMD_CACHE passthrough
plugins: Implement no-op .cache for in-memory plugins
sh: Implement .cache script callback
filters: Add .cache callback
test-layers: Test .cache usage
blocksize: Implement .cache rounding
docs/nbdkit-filter.pod | 27 ++++++++++++++-
docs/nbdkit-plugin.pod | 52 ++++++++++++++++++++++++++++
docs/nbdkit-protocol.pod | 10 ++++++
plugins/sh/nbdkit-sh-plugin.pod | 12 ++++++-
configure.ac | 3 +-
common/protocol/protocol.h | 2 ++
include/nbdkit-filter.h | 8 +++++
include/nbdkit-plugin.h | 2 ++
server/internal.h | 4 +++
filters/blocksize/blocksize.c | 31 ++++++++++++++++-
plugins/data/data.c | 10 ++++++
plugins/file/file.c | 22 ++++++++++++
plugins/full/full.c | 12 ++++++-
plugins/memory/memory.c | 10 ++++++
plugins/nbd/nbd.c | 22 ++++++++++++
plugins/null/null.c | 12 ++++++-
plugins/pattern/pattern.c | 12 ++++++-
plugins/random/random.c | 12 ++++++-
plugins/sh/sh.c | 40 ++++++++++++++++++++++
plugins/split/split.c | 37 +++++++++++++++++++-
plugins/streaming/streaming.c | 11 ++++++
plugins/zero/zero.c | 12 ++++++-
server/filters.c | 60 ++++++++++++++++++++++++++++++++-
server/plugins.c | 39 +++++++++++++++++++++
server/protocol-handshake.c | 10 +++++-
server/protocol.c | 25 ++++++++++++++
tests/test-layers-filter.c | 22 +++++++++++-
tests/test-layers-plugin.c | 17 ++++++++++
tests/test-layers.c | 36 ++++++++++++++++++++
tests/test-eflags.sh | 53 +++++++++++++++--------------
30 files changed, 587 insertions(+), 38 deletions(-)
--
2.20.1
10:03 p.m.
New subject: [nbdkit PATCH 1/9] server: Internal hooks for implementing NBD_CMD_CACHE
Until the next few patches expose and implement new callbacks for
filters and plugins, our initial implementation for NBD_CMD_CACHE is
to just blindly advertise the feature, and call into .pread with an
ignored buffer.
Note that for bisection reasons, this patch treats any use of a filter
as a forced .can_cache of false to bypass the filter's caching; once
all affected filters are patched to handle cache requests correctly, a
later patch will then switch the filter default to passthrough for the
sake of remaining filters.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
Note: we could also choose to always advertise caching, but make the
nbdkit default version be a no-op rather than call out to .pread. For
that matter, maybe a plugin's .can_cache should allow the plugin to
choose between a tri-state of no-op, fallback to .pread, or call
.cache; I'm not sure which is the saner default for a random plugin
compiled against older nbdkit. At least it's fairly easy to write a
filter that changes the default from no-op to .pread or from .pread to
no-op. Be thinking about that as you review the rest of the series.
---
docs/nbdkit-protocol.pod | 10 +++++++
common/protocol/protocol.h | 2 ++
server/internal.h | 4 +++
server/filters.c | 33 ++++++++++++++++++++++-
server/plugins.c | 34 ++++++++++++++++++++++++
server/protocol-handshake.c | 10 ++++++-
server/protocol.c | 25 +++++++++++++++++
tests/test-eflags.sh | 53 ++++++++++++++++++++-----------------
8 files changed, 144 insertions(+), 27 deletions(-)
diff --git a/docs/nbdkit-protocol.pod b/docs/nbdkit-protocol.pod
index f706cfd..6b85c14 100644
--- a/docs/nbdkit-protocol.pod
+++ b/docs/nbdkit-protocol.pod
@@ -152,6 +152,16 @@ when structured replies are in effect. However, the flag is a no-op
until we extend the plugin API to allow a fragmented read in the first
place.
+=item C<NBD_CMD_CACHE>
+
+Supported in nbdkit E<ge> 1.13.4.
+
+This protocol extension allows a client to inform the server about
+intent to access a portion of the export, to allow the server an
+opportunity to cache things appropriately. For plugins that do not
+support a particular form of caching, nbdkit performs pread then
+ignores the results.
+
=item Resize Extension
I<Not supported>.
diff --git a/common/protocol/protocol.h b/common/protocol/protocol.h
index c27104c..e938643 100644
--- a/common/protocol/protocol.h
+++ b/common/protocol/protocol.h
@@ -95,6 +95,7 @@ extern const char *name_of_nbd_flag (int);
#define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6)
#define NBD_FLAG_SEND_DF (1 << 7)
#define NBD_FLAG_CAN_MULTI_CONN (1 << 8)
+#define NBD_FLAG_SEND_CACHE (1 << 10)
/* NBD options (new style handshake only). */
extern const char *name_of_nbd_opt (int);
@@ -217,6 +218,7 @@ extern const char *name_of_nbd_cmd (int);
#define NBD_CMD_DISC 2 /* Disconnect. */
#define NBD_CMD_FLUSH 3
#define NBD_CMD_TRIM 4
+#define NBD_CMD_CACHE 5
#define NBD_CMD_WRITE_ZEROES 6
#define NBD_CMD_BLOCK_STATUS 7
diff --git a/server/internal.h b/server/internal.h
index 67fccfc..6414a78 100644
--- a/server/internal.h
+++ b/server/internal.h
@@ -170,6 +170,7 @@ struct connection {
bool can_zero;
bool can_fua;
bool can_multi_conn;
+ bool can_cache;
bool can_extents;
bool using_tls;
bool structured_replies;
@@ -276,6 +277,7 @@ struct backend {
int (*can_extents) (struct backend *, struct connection *conn);
int (*can_fua) (struct backend *, struct connection *conn);
int (*can_multi_conn) (struct backend *, struct connection *conn);
+ int (*can_cache) (struct backend *, struct connection *conn);
int (*pread) (struct backend *, struct connection *conn, void *buf,
uint32_t count, uint64_t offset, uint32_t flags, int *err);
@@ -290,6 +292,8 @@ struct backend {
int (*extents) (struct backend *, struct connection *conn, uint32_t count,
uint64_t offset, uint32_t flags,
struct nbdkit_extents *extents, int *err);
+ int (*cache) (struct backend *, struct connection *conn, uint32_t count,
+ uint64_t offset, uint32_t flags, int *err);
};
/* plugins.c */
diff --git a/server/filters.c b/server/filters.c
index b73e74f..c619fd6 100644
--- a/server/filters.c
+++ b/server/filters.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2013-2018 Red Hat Inc.
+ * Copyright (C) 2013-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -573,6 +573,18 @@ filter_can_multi_conn (struct backend *b, struct connection *conn)
return f->backend.next->can_multi_conn (f->backend.next, conn);
}
+static int
+filter_can_cache (struct backend *b, struct connection *conn)
+{
+ struct backend_filter *f = container_of (b, struct backend_filter, backend);
+
+ debug ("%s: can_cache", f->name);
+
+ /* FIXME: Default to f->backend.next->can_cache, once all filters
+ have been audited */
+ return 0;
+}
+
static int
filter_pread (struct backend *b, struct connection *conn,
void *buf, uint32_t count, uint64_t offset,
@@ -702,6 +714,23 @@ filter_extents (struct backend *b, struct connection *conn,
extents, err);
}
+static int
+filter_cache (struct backend *b, struct connection *conn,
+ uint32_t count, uint64_t offset,
+ uint32_t flags, int *err)
+{
+ struct backend_filter *f = container_of (b, struct backend_filter, backend);
+
+ assert (flags == 0);
+
+ debug ("%s: cache count=%" PRIu32 " offset=%" PRIu64 "
flags=0x%" PRIx32,
+ f->name, count, offset, flags);
+
+ /* FIXME: Allow filter to rewrite request */
+ return f->backend.next->cache (f->backend.next, conn,
+ count, offset, flags, err);
+}
+
static struct backend filter_functions = {
.free = filter_free,
.thread_model = filter_thread_model,
@@ -726,12 +755,14 @@ static struct backend filter_functions = {
.can_extents = filter_can_extents,
.can_fua = filter_can_fua,
.can_multi_conn = filter_can_multi_conn,
+ .can_cache = filter_can_cache,
.pread = filter_pread,
.pwrite = filter_pwrite,
.flush = filter_flush,
.trim = filter_trim,
.zero = filter_zero,
.extents = filter_extents,
+ .cache = filter_cache,
};
/* Register and load a filter. */
diff --git a/server/plugins.c b/server/plugins.c
index e26d133..cabf543 100644
--- a/server/plugins.c
+++ b/server/plugins.c
@@ -448,6 +448,17 @@ plugin_can_multi_conn (struct backend *b, struct connection *conn)
return 0; /* assume false */
}
+static int
+plugin_can_cache (struct backend *b, struct connection *conn)
+{
+ assert (connection_get_handle (conn, 0));
+
+ debug ("can_cache");
+
+ /* FIXME: return default based on plugin->cache */
+ return 0;
+}
+
/* Plugins and filters can call this to set the true errno, in cases
* where !errno_is_preserved.
*/
@@ -693,6 +704,27 @@ plugin_extents (struct backend *b, struct connection *conn,
return r;
}
+static int
+plugin_cache (struct backend *b, struct connection *conn,
+ uint32_t count, uint64_t offset, uint32_t flags,
+ int *err)
+{
+ struct backend_plugin *p = container_of (b, struct backend_plugin, backend);
+ int r = -1;
+
+ assert (connection_get_handle (conn, 0));
+ assert (!flags);
+
+ debug ("cache count=%" PRIu32 " offset=%" PRIu64, count, offset);
+
+ /* FIXME: assert plugin->cache and call it */
+ assert (false);
+
+ if (r == -1)
+ *err = get_error (p);
+ return r;
+}
+
static struct backend plugin_functions = {
.free = plugin_free,
.thread_model = plugin_thread_model,
@@ -717,12 +749,14 @@ static struct backend plugin_functions = {
.can_extents = plugin_can_extents,
.can_fua = plugin_can_fua,
.can_multi_conn = plugin_can_multi_conn,
+ .can_cache = plugin_can_cache,
.pread = plugin_pread,
.pwrite = plugin_pwrite,
.flush = plugin_flush,
.trim = plugin_trim,
.zero = plugin_zero,
.extents = plugin_extents,
+ .cache = plugin_cache,
};
/* Register and load a plugin. */
diff --git a/server/protocol-handshake.c b/server/protocol-handshake.c
index 03377a9..af1cd18 100644
--- a/server/protocol-handshake.c
+++ b/server/protocol-handshake.c
@@ -109,7 +109,7 @@ protocol_compute_eflags (struct connection *conn, uint16_t *flags)
conn->can_multi_conn = true;
}
- /* The result of this is not returned to callers here (or at any
+ /* The results of the next two are not returned to callers here (or at any
* time during the handshake). However it makes sense to do it once
* per connection and store the result in the handle anyway. This
* protocol_compute_eflags function is a bit misnamed XXX.
@@ -120,6 +120,14 @@ protocol_compute_eflags (struct connection *conn, uint16_t *flags)
if (fl)
conn->can_extents = true;
+ fl = backend->can_cache (backend, conn);
+ if (fl == -1)
+ return -1;
+ if (fl)
+ conn->can_cache = true;
+ /* We emulate cache even when plugin doesn't support it */
+ eflags |= NBD_FLAG_SEND_CACHE;
+
if (conn->structured_replies)
eflags |= NBD_FLAG_SEND_DF;
diff --git a/server/protocol.c b/server/protocol.c
index 01d4c71..69227e5 100644
--- a/server/protocol.c
+++ b/server/protocol.c
@@ -76,6 +76,7 @@ validate_request (struct connection *conn,
/* Validate cmd, offset, count. */
switch (cmd) {
case NBD_CMD_READ:
+ case NBD_CMD_CACHE:
case NBD_CMD_WRITE:
case NBD_CMD_TRIM:
case NBD_CMD_WRITE_ZEROES:
@@ -254,6 +255,30 @@ handle_request (struct connection *conn,
return err;
break;
+ case NBD_CMD_CACHE:
+ /* The other backend methods don't check can_*. That is because
+ * those methods are implicitly suppressed by returning fewer
+ * eflags to the client. However the eflag for cache is always
+ * sent, because we emulate it here when the plugin lacks it.
+ */
+ if (conn->can_cache) {
+ if (backend->cache (backend, conn, count, offset, 0, &err) == -1)
+ return err;
+ }
+ else {
+ static char buf[MAX_REQUEST_SIZE]; /* data sink, never read */
+ uint32_t limit;
+
+ while (count) {
+ limit = MIN (count, sizeof buf);
+ if (backend->pread (backend, conn, buf, limit, offset, flags,
+ &err) == -1)
+ return err;
+ count -= limit;
+ }
+ }
+ break;
+
case NBD_CMD_WRITE_ZEROES:
if (!(flags & NBD_CMD_FLAG_NO_HOLE))
f |= NBDKIT_FLAG_MAY_TRIM;
diff --git a/tests/test-eflags.sh b/tests/test-eflags.sh
index 84dcfe8..0234aca 100755
--- a/tests/test-eflags.sh
+++ b/tests/test-eflags.sh
@@ -1,6 +1,6 @@
#!/usr/bin/env bash
# nbdkit
-# Copyright (C) 2018 Red Hat Inc.
+# Copyright (C) 2018-2019 Red Hat Inc.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
@@ -94,8 +94,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# -r
@@ -108,8 +108,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# can_write=true
@@ -126,8 +126,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# -r
@@ -144,8 +144,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# can_write=false
@@ -164,8 +164,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# -r
@@ -185,8 +185,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# can_write=true
@@ -201,8 +201,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# can_write=true
@@ -217,8 +217,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# -r
@@ -234,8 +234,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|ROTATIONAL|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|ROTATIONAL|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|ROTATIONAL|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|ROTATIONAL|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# can_write=true
@@ -250,8 +250,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# -r
@@ -269,8 +269,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|SEND_CACHE"
#----------------------------------------------------------------------
# -r
@@ -284,5 +284,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|CAN_MULTI_CONN )) ] ||
- fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|CAN_MULTI_CONN"
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF|CAN_MULTI_CONN|SEND_CACHE )) ] ||
+ fail "expected HAS_FLAGS|READ_ONLY|SEND_DF|CAN_MULTI_CONN|SEND_CACHE"
+
+# NBD_FLAG_SEND_CACHE is always set even if can_cache returns false, because
+# nbdkit reckons it can emulate caching using pread.
--
2.20.1
2:56 a.m.
New subject: [nbdkit PATCH 1/9] server: Internal hooks for implementing NBD_CMD_CACHE
On Thu, May 09, 2019 at 10:03:34PM -0500, Eric Blake wrote:
Until the next few patches expose and implement new callbacks for
filters and plugins, our initial implementation for NBD_CMD_CACHE is
to just blindly advertise the feature, and call into .pread with an
ignored buffer.
Note that for bisection reasons, this patch treats any use of a filter
as a forced .can_cache of false to bypass the filter's caching; once
all affected filters are patched to handle cache requests correctly, a
later patch will then switch the filter default to passthrough for the
sake of remaining filters.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
Note: we could also choose to always advertise caching, but make the
nbdkit default version be a no-op rather than call out to .pread. For
that matter, maybe a plugin's .can_cache should allow the plugin to
choose between a tri-state of no-op, fallback to .pread, or call
.cache; I'm not sure which is the saner default for a random plugin
compiled against older nbdkit. At least it's fairly easy to write a
filter that changes the default from no-op to .pread or from .pread to
no-op. Be thinking about that as you review the rest of the series.
I'm worried that we end up in the same situation that we do with
.zero: because we emulate it, we end up with a slow zero support,
whereas clients [well, Nir S. mainly] actually want
NBD_FLAG_SEND_WRITE_ZEROES == *fast* zeroing is available.
In particular in the NBD_CMD_CACHE case: for some plugins emulating
this behind the scenes with pread makes some sense. eg. It works for
nbdkit-file-plugin because it will prefetch the data into Linux's page
cache. However if a plugin makes a network access,
eg. nbdkit-vddk-plugin, that can be both very expensive and has no
prefetching benefit.
Therefore I do think we should default to ignoring NBD_CMD_CACHE
commands and *not* advertising the feature, except when the plugin
says that it is able to handle it.
For tri-stating .can_cache: yes that makes sense, because there is
moderate difficulty for a plugin to emulate .cache using .pread. The
plugin has to at least allocate a dummy buffer and throw it away, and
we could probably do something more efficient than that if we
implement an emulate mode in the server.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine. Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/
9:14 a.m.
New subject: [nbdkit PATCH 1/9] server: Internal hooks for implementing NBD_CMD_CACHE
On 5/13/19 2:56 AM, Richard W.M. Jones wrote:
On Thu, May 09, 2019 at 10:03:34PM -0500, Eric Blake wrote:
> Until the next few patches expose and implement new callbacks for
> filters and plugins, our initial implementation for NBD_CMD_CACHE is
> to just blindly advertise the feature, and call into .pread with an
> ignored buffer.
>
> Note that for bisection reasons, this patch treats any use of a filter
> as a forced .can_cache of false to bypass the filter's caching; once
> all affected filters are patched to handle cache requests correctly, a
> later patch will then switch the filter default to passthrough for the
> sake of remaining filters.
>
> Signed-off-by: Eric Blake <eblake(a)redhat.com>
>
> ---
>
> Note: we could also choose to always advertise caching, but make the
> nbdkit default version be a no-op rather than call out to .pread. For
> that matter, maybe a plugin's .can_cache should allow the plugin to
> choose between a tri-state of no-op, fallback to .pread, or call
> .cache; I'm not sure which is the saner default for a random plugin
> compiled against older nbdkit. At least it's fairly easy to write a
> filter that changes the default from no-op to .pread or from .pread to
> no-op. Be thinking about that as you review the rest of the series.
I'm worried that we end up in the same situation that we do with
.zero: because we emulate it, we end up with a slow zero support,
whereas clients [well, Nir S. mainly] actually want
NBD_FLAG_SEND_WRITE_ZEROES == *fast* zeroing is available.
Yes, I still need to revisit my NBD protocol proposal for an additional
flag during WRITE_ZEROES for a client to easily get fast failure if it
would otherwise be emulated. It may make .can_zero turn into tri-state :)
In particular in the NBD_CMD_CACHE case: for some plugins emulating
this behind the scenes with pread makes some sense. eg. It works for
nbdkit-file-plugin because it will prefetch the data into Linux's page
cache. However if a plugin makes a network access,
eg. nbdkit-vddk-plugin, that can be both very expensive and has no
prefetching benefit.
Therefore I do think we should default to ignoring NBD_CMD_CACHE
commands and *not* advertising the feature, except when the plugin
says that it is able to handle it.
For tri-stating .can_cache: yes that makes sense, because there is
moderate difficulty for a plugin to emulate .cache using .pread. The
plugin has to at least allocate a dummy buffer and throw it away, and
we could probably do something more efficient than that if we
implement an emulate mode in the server.
Okay, I'll rework the series along those lines, where .can_cache has to
be set for a plugin/filter to opt-in to advertising the feature to
clients (rather than always blindly advertising it).
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
10:03 p.m.
New subject: [nbdkit PATCH 2/9] plugins: Add .cache callback
Make it possible for plugins to provide an alternative behavior for
NBD_CMD_CACHE rather than just discarding the buffer of .pread.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
docs/nbdkit-plugin.pod | 52 +++++++++++++++++++++++++++++++++++++++++
include/nbdkit-plugin.h | 2 ++
server/plugins.c | 17 +++++++++-----
3 files changed, 65 insertions(+), 6 deletions(-)
diff --git a/docs/nbdkit-plugin.pod b/docs/nbdkit-plugin.pod
index 318be4c..0657151 100644
--- a/docs/nbdkit-plugin.pod
+++ b/docs/nbdkit-plugin.pod
@@ -620,6 +620,31 @@ with an error message and return C<-1>.
This callback is not required. If omitted, then we return false.
+=head2 C<.can_cache>
+
+ int can_cache (void *handle);
+
+This is called during the option negotiation phase to find out if the
+plugin supports a cache operation. The nature of the caching is
+unspecified (including whether there are limits on how much can be
+cached at once, and whether writes to a cached region have
+write-through or write-back semantics), but the command exists to let
+clients issue a hint to the server that they will be accessing that
+region of the export.
+
+If there is an error, C<.can_cache> should call C<nbdkit_error> with
+an error message and return C<-1>. Since the NBD protocol has
+reserved the right to add future flags to mandate specific caching
+capabilities, this function should only return C<1> on success (in the
+future, other positive results may be treated as a bitmask of
+supported flags).
+
+This callback is not required. If omitted, then we return true iff a
+C<.cache> callback has been defined. Note that nbdkit always
+advertises caching capabilities to the client regardless of this
+callback; if this callback returns false, nbdkit handles a client
+cache request by calling C<.pread> and ignoring the resulting data.
+
=head2 C<.pread>
int pread (void *handle, void *buf, uint32_t count, uint64_t offset,
@@ -814,6 +839,33 @@ C<nbdkit_extent_add> returns C<0> on success or
C<-1> on failure. On
failure C<nbdkit_error> and/or C<nbdkit_set_error> has already been
called. C<errno> will be set to a suitable value.
+=head2 C<.cache>
+
+ int cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags);
+
+During the data serving phase, this callback is used to give the
+plugin a hint that the client intends to make further accesses to the
+given region of the export. The nature of caching is not specified
+further by the NBD specification (for example, a server may place
+limits on how much may be cached at once, and there is no way to
+control if writes to a cached area have write-through or write-back
+semantics). In fact, the cache command can always fail and still be
+compliant, and success might not guarantee a performance gain. If
+this callback is omitted, nbdkit defaults to providing cache semantics
+obtained by calling C<.pread> over the same region and ignoring the
+results.
+
+This function will not be called if C<.can_cache> returned false. The
+parameter C<flags> exists in case of future NBD protocol extensions;
+at this time, it will be 0 on input. A plugin must fail this function
+if C<flags> includes an unrecognized flag, as that may indicate a
+requirement that the plugin comply must with a specific caching
+semantic.
+
+If there is an error, C<.cache> should call C<nbdkit_error> with an
+error message, and C<nbdkit_set_error> to record an appropriate error
+(unless C<errno> is sufficient), then return C<-1>.
+
=head1 THREADS
Each nbdkit plugin must declare its thread safety model by defining
diff --git a/include/nbdkit-plugin.h b/include/nbdkit-plugin.h
index 54b4ce2..e9b1808 100644
--- a/include/nbdkit-plugin.h
+++ b/include/nbdkit-plugin.h
@@ -128,6 +128,8 @@ struct nbdkit_plugin {
int (*can_extents) (void *handle);
int (*extents) (void *handle, uint32_t count, uint64_t offset, uint32_t flags,
struct nbdkit_extents *extents);
+ int (*can_cache) (void *handle);
+ int (*cache) (void *handle, uint32_t count, uint64_t offset, uint32_t flags);
};
extern void nbdkit_set_error (int err);
diff --git a/server/plugins.c b/server/plugins.c
index cabf543..947fe79 100644
--- a/server/plugins.c
+++ b/server/plugins.c
@@ -201,6 +201,8 @@ plugin_dump_fields (struct backend *b)
HAS (can_multi_conn);
HAS (can_extents);
HAS (extents);
+ HAS (can_cache);
+ HAS (cache);
#undef HAS
/* Custom fields. */
@@ -451,12 +453,16 @@ plugin_can_multi_conn (struct backend *b, struct connection *conn)
static int
plugin_can_cache (struct backend *b, struct connection *conn)
{
+ struct backend_plugin *p = container_of (b, struct backend_plugin, backend);
+
assert (connection_get_handle (conn, 0));
debug ("can_cache");
- /* FIXME: return default based on plugin->cache */
- return 0;
+ if (p->plugin.can_cache)
+ return p->plugin.can_cache (connection_get_handle (conn, 0));
+ else
+ return p->plugin.cache != NULL;
}
/* Plugins and filters can call this to set the true errno, in cases
@@ -710,16 +716,15 @@ plugin_cache (struct backend *b, struct connection *conn,
int *err)
{
struct backend_plugin *p = container_of (b, struct backend_plugin, backend);
- int r = -1;
+ int r;
assert (connection_get_handle (conn, 0));
assert (!flags);
+ assert (p->plugin.cache);
debug ("cache count=%" PRIu32 " offset=%" PRIu64, count, offset);
- /* FIXME: assert plugin->cache and call it */
- assert (false);
-
+ r = p->plugin.cache (connection_get_handle (conn, 0), count, offset, flags);
if (r == -1)
*err = get_error (p);
return r;
--
2.20.1
10:03 p.m.
New subject: [nbdkit PATCH 3/9] file, split: Implement .cache with posix_fadvise
Since NBD_CMD_CACHE is already advisory, let's use an advisory kernel
interface to implement it ;) When posix_fadvise() is not present, it
is likely that nbdkit's fallback to .pread will actually have a
similar benefit in populating the filesystem cache, since we aren't
using O_DIRECT to avoid that cache.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
configure.ac | 3 ++-
plugins/file/file.c | 22 ++++++++++++++++++++++
plugins/split/split.c | 37 ++++++++++++++++++++++++++++++++++++-
3 files changed, 60 insertions(+), 2 deletions(-)
diff --git a/configure.ac b/configure.ac
index 58031f3..06124c5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -195,7 +195,8 @@ dnl Check for functions in libc, all optional.
AC_CHECK_FUNCS([\
fdatasync \
get_current_dir_name \
- mkostemp])
+ mkostemp \
+ posix_fadvise])
dnl Check whether printf("%m") works
AC_CACHE_CHECK([whether the printf family supports %m],
diff --git a/plugins/file/file.c b/plugins/file/file.c
index f0ac23b..85b033b 100644
--- a/plugins/file/file.c
+++ b/plugins/file/file.c
@@ -608,6 +608,25 @@ file_extents (void *handle, uint32_t count, uint64_t offset,
}
#endif /* SEEK_HOLE */
+#if HAVE_POSIX_FADVISE
+/* Caching. */
+static int
+file_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ struct handle *h = handle;
+ int r;
+
+ /* Cache is advisory, we don't care if this fails */
+ r = posix_fadvise (h->fd, offset, count, POSIX_FADV_WILLNEED);
+ if (r) {
+ errno = r;
+ nbdkit_error ("posix_fadvise: %m");
+ return -1;
+ }
+ return 0;
+}
+#endif /* HAVE_POSIX_FADVISE */
+
static struct nbdkit_plugin plugin = {
.name = "file",
.longname = "nbdkit file plugin",
@@ -632,6 +651,9 @@ static struct nbdkit_plugin plugin = {
#ifdef SEEK_HOLE
.can_extents = file_can_extents,
.extents = file_extents,
+#endif
+#if HAVE_POSIX_FADVISE
+ .cache = file_cache,
#endif
.errno_is_preserved = 1,
};
diff --git a/plugins/split/split.c b/plugins/split/split.c
index cf2b2c7..cef2d51 100644
--- a/plugins/split/split.c
+++ b/plugins/split/split.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -277,6 +277,38 @@ split_pwrite (void *handle, const void *buf, uint32_t count, uint64_t
offset)
return 0;
}
+#if HAVE_POSIX_FADVISE
+/* Caching. */
+static int
+split_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ struct handle *h = handle;
+
+ /* Cache is advisory, we don't care if this fails */
+ while (count > 0) {
+ struct file *file = get_file (h, offset);
+ uint64_t foffs = offset - file->offset;
+ uint64_t max;
+ int r;
+
+ max = file->size - foffs;
+ if (max > count)
+ max = count;
+
+ r = posix_fadvise (file->fd, offset, max, POSIX_FADV_WILLNEED);
+ if (r) {
+ errno = r;
+ nbdkit_error ("posix_fadvise: %m");
+ return -1;
+ }
+ count -= r;
+ offset += r;
+ }
+
+ return 0;
+}
+#endif /* HAVE_POSIX_FADVISE */
+
static struct nbdkit_plugin plugin = {
.name = "split",
.version = PACKAGE_VERSION,
@@ -289,6 +321,9 @@ static struct nbdkit_plugin plugin = {
.get_size = split_get_size,
.pread = split_pread,
.pwrite = split_pwrite,
+#if HAVE_POSIX_FADVISE
+ .cache = split_cache,
+#endif
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
--
2.20.1
10:03 p.m.
New subject: [nbdkit PATCH 4/9] nbd: Implement NBD_CMD_CACHE passthrough
In the nbd plugin, if the remote server supports any form of caching,
we should utilize that rather than nbdkit's fallback to .pread.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
plugins/nbd/nbd.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c
index 821f256..71549d7 100644
--- a/plugins/nbd/nbd.c
+++ b/plugins/nbd/nbd.c
@@ -1151,6 +1151,14 @@ nbd_can_multi_conn (void *handle)
return h->flags & NBD_FLAG_CAN_MULTI_CONN;
}
+static int
+nbd_can_cache (void *handle)
+{
+ struct handle *h = handle;
+
+ return h->flags & NBD_FLAG_SEND_CACHE;
+}
+
static int
nbd_can_extents (void *handle)
{
@@ -1245,6 +1253,18 @@ nbd_extents (void *handle, uint32_t count, uint64_t offset,
return c < 0 ? c : nbd_reply (h, c);
}
+/* Cache a portion of the file. */
+static int
+nbd_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ struct handle *h = handle;
+ int c;
+
+ assert (!flags);
+ c = nbd_request (h, 0, NBD_CMD_CACHE, offset, count);
+ return c < 0 ? c : nbd_reply (h, c);
+}
+
static struct nbdkit_plugin plugin = {
.name = "nbd",
.longname = "nbdkit nbd plugin",
@@ -1264,12 +1284,14 @@ static struct nbdkit_plugin plugin = {
.can_fua = nbd_can_fua,
.can_multi_conn = nbd_can_multi_conn,
.can_extents = nbd_can_extents,
+ .can_cache = nbd_can_cache,
.pread = nbd_pread,
.pwrite = nbd_pwrite,
.zero = nbd_zero,
.flush = nbd_flush,
.trim = nbd_trim,
.extents = nbd_extents,
+ .cache = nbd_cache,
.errno_is_preserved = 1,
};
--
2.20.1
10:03 p.m.
New subject: [nbdkit PATCH 5/9] plugins: Implement no-op .cache for in-memory plugins
For our plugins which have no backing file but generate everything on
the fly or store things in memory, falling back to .pread on a cache
request is just wasted work. Implement a no-op .cache callback for the
drivers where there is no benefit to trying to cache anything.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
plugins/data/data.c | 10 ++++++++++
plugins/full/full.c | 12 +++++++++++-
plugins/memory/memory.c | 10 ++++++++++
plugins/null/null.c | 12 +++++++++++-
plugins/pattern/pattern.c | 12 +++++++++++-
plugins/random/random.c | 12 +++++++++++-
plugins/streaming/streaming.c | 11 +++++++++++
plugins/zero/zero.c | 12 +++++++++++-
8 files changed, 86 insertions(+), 5 deletions(-)
diff --git a/plugins/data/data.c b/plugins/data/data.c
index 55380c6..aaa3d2d 100644
--- a/plugins/data/data.c
+++ b/plugins/data/data.c
@@ -377,6 +377,15 @@ data_extents (void *handle, uint32_t count, uint64_t offset,
return sparse_array_extents (sa, count, offset, extents);
}
+/* Cache. */
+static int
+data_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* Everything is already in memory, falling back to .pread is
+ actually slower than treating this as a no-op. */
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "data",
.version = PACKAGE_VERSION,
@@ -394,6 +403,7 @@ static struct nbdkit_plugin plugin = {
.zero = data_zero,
.trim = data_trim,
.extents = data_extents,
+ .cache = data_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
diff --git a/plugins/full/full.c b/plugins/full/full.c
index 7661856..51a9d67 100644
--- a/plugins/full/full.c
+++ b/plugins/full/full.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -137,6 +137,15 @@ full_extents (void *handle, uint32_t count, uint64_t offset, uint32_t
flags,
NBDKIT_EXTENT_HOLE | NBDKIT_EXTENT_ZERO);
}
+/* Cache. */
+static int
+full_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* Everything is already in memory, falling back to .pread is
+ actually slower than treating this as a no-op. */
+ return 0;
+}
+
/* Note that we don't need to handle flush: If there has been previous
* write then we have already returned an error. If there have been
* no previous writes then flush can be ignored.
@@ -156,6 +165,7 @@ static struct nbdkit_plugin plugin = {
.zero = full_zero,
.trim = full_trim,
.extents = full_extents,
+ .cache = full_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
diff --git a/plugins/memory/memory.c b/plugins/memory/memory.c
index 90fa99e..baa29e2 100644
--- a/plugins/memory/memory.c
+++ b/plugins/memory/memory.c
@@ -172,6 +172,15 @@ memory_extents (void *handle, uint32_t count, uint64_t offset,
return sparse_array_extents (sa, count, offset, extents);
}
+/* Cache. */
+static int
+memory_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* Everything is already in memory, falling back to .pread is
+ actually slower than treating this as a no-op. */
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "memory",
.version = PACKAGE_VERSION,
@@ -189,6 +198,7 @@ static struct nbdkit_plugin plugin = {
.zero = memory_zero,
.trim = memory_trim,
.extents = memory_extents,
+ .cache = memory_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
diff --git a/plugins/null/null.c b/plugins/null/null.c
index 518b63b..5e40868 100644
--- a/plugins/null/null.c
+++ b/plugins/null/null.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -140,6 +140,15 @@ null_extents (void *handle, uint32_t count, uint64_t offset, uint32_t
flags,
NBDKIT_EXTENT_HOLE | NBDKIT_EXTENT_ZERO);
}
+/* Cache. */
+static int
+null_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* Everything is already in memory, falling back to .pread is
+ actually slower than treating this as a no-op. */
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "null",
.version = PACKAGE_VERSION,
@@ -155,6 +164,7 @@ static struct nbdkit_plugin plugin = {
.can_fua = null_can_fua,
.flush = null_flush,
.extents = null_extents,
+ .cache = null_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
diff --git a/plugins/pattern/pattern.c b/plugins/pattern/pattern.c
index 115bd96..e25da36 100644
--- a/plugins/pattern/pattern.c
+++ b/plugins/pattern/pattern.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -117,6 +117,15 @@ pattern_pread (void *handle, void *buf, uint32_t count, uint64_t
offset,
return 0;
}
+/* Cache. */
+static int
+pattern_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* Everything is already in memory, falling back to .pread is
+ actually slower than treating this as a no-op. */
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "pattern",
.version = PACKAGE_VERSION,
@@ -127,6 +136,7 @@ static struct nbdkit_plugin plugin = {
.get_size = pattern_get_size,
.can_multi_conn = pattern_can_multi_conn,
.pread = pattern_pread,
+ .cache = pattern_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
diff --git a/plugins/random/random.c b/plugins/random/random.c
index 7fb42c8..6219169 100644
--- a/plugins/random/random.c
+++ b/plugins/random/random.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -146,6 +146,15 @@ random_pread (void *handle, void *buf, uint32_t count, uint64_t
offset,
return 0;
}
+/* Cache. */
+static int
+random_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* Everything is already in memory, falling back to .pread is
+ actually slower than treating this as a no-op. */
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "random",
.version = PACKAGE_VERSION,
@@ -157,6 +166,7 @@ static struct nbdkit_plugin plugin = {
.get_size = random_get_size,
.can_multi_conn = random_can_multi_conn,
.pread = random_pread,
+ .cache = random_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
diff --git a/plugins/streaming/streaming.c b/plugins/streaming/streaming.c
index 4ca3e76..505ed91 100644
--- a/plugins/streaming/streaming.c
+++ b/plugins/streaming/streaming.c
@@ -246,6 +246,16 @@ streaming_pread (void *handle, void *buf, uint32_t count, uint64_t
offset)
return -1;
}
+/* Cache. */
+static int
+streaming_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* nbdkit's default of falling back to .pread is pointless: it will
+ * fail for addresses already written, and waste a memset() for
+ * addresses not yet reached. Treat this as a no-op instead. */
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "streaming",
.longname = "nbdkit streaming plugin",
@@ -259,6 +269,7 @@ static struct nbdkit_plugin plugin = {
.get_size = streaming_get_size,
.pwrite = streaming_pwrite,
.pread = streaming_pread,
+ .cache = streaming_cache,
.errno_is_preserved = 1,
};
diff --git a/plugins/zero/zero.c b/plugins/zero/zero.c
index 49ce08e..be8fc2a 100644
--- a/plugins/zero/zero.c
+++ b/plugins/zero/zero.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -76,6 +76,15 @@ zero_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
return -1;
}
+/* Cache. */
+static int
+zero_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ /* Everything is already in memory, falling back to .pread is
+ actually slower than treating this as a no-op. */
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "zero",
.version = PACKAGE_VERSION,
@@ -83,6 +92,7 @@ static struct nbdkit_plugin plugin = {
.open = zero_open,
.get_size = zero_get_size,
.pread = zero_pread,
+ .cache = zero_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
--
2.20.1
10:03 p.m.
New subject: [nbdkit PATCH 6/9] sh: Implement .cache script callback
It's easy to expose new callbacks to sh plugins. I have no idea how
any plugin would actually usefully cache anything in shell (you can't
really store it in a shell variable, since a new shell process is
started for each command); but if nothing else, this allows a user to
implement .can_cache returning true to bypass nbdkit's normal fallback
to .pread.
The shell plugin, coupled with Rich's work on libnbd as a client-side
library for actually exercising calls to NBD_CMD_CACHE, will be a
useful way to prove that cache commands even make it through the
stack. (Remember, qemu 3.0 was released with a fatally flawed
NBD_CMD_CACHE server implementation, because there were no open source
clients at the time that could actually send the command to test the
server with).
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
plugins/sh/nbdkit-sh-plugin.pod | 12 +++++++++-
plugins/sh/sh.c | 40 +++++++++++++++++++++++++++++++++
2 files changed, 51 insertions(+), 1 deletion(-)
diff --git a/plugins/sh/nbdkit-sh-plugin.pod b/plugins/sh/nbdkit-sh-plugin.pod
index 8af88b4..bfd58ab 100644
--- a/plugins/sh/nbdkit-sh-plugin.pod
+++ b/plugins/sh/nbdkit-sh-plugin.pod
@@ -218,9 +218,11 @@ This method is required.
=item C<can_extents>
+=item C<can_cache>
+
Unlike in other languages, you B<must> provide the C<can_*> methods
otherwise they are assumed to all return false and your C<pwrite>,
-C<flush>, C<trim>, C<zero> and C<extents> methods will never be
+C<flush>, C<trim>, C<zero>, C<extents>, and C<cache>
methods will never be
called. The reason for this is obscure: In other languages we can
detect if (eg) a C<pwrite> method is defined and synthesize an
appropriate response if no actual C<can_write> method is defined.
@@ -232,6 +234,7 @@ possible with this plugin.
/path/to/script can_trim <handle>
/path/to/script can_zero <handle>
/path/to/script can_extents <handle>
+ /path/to/script can_cache <handle>
The script should exit with code C<0> for true or code C<3> for false.
@@ -334,6 +337,13 @@ Unlike in other languages, if you provide an C<extents> method
you
B<must> also provide a C<can_extents> method which exits with code
C<0> (true).
+=item C<cache>
+
+ /path/to/script cache <handle> <count> <offset>
+
+Unlike in other languages, if you provide a C<cache> method you B<must>
+also provide a C<can_cache> method which exits with code C<0> (true).
+
=back
=head2 Missing callbacks
diff --git a/plugins/sh/sh.c b/plugins/sh/sh.c
index a5beb57..7aded44 100644
--- a/plugins/sh/sh.c
+++ b/plugins/sh/sh.c
@@ -578,6 +578,12 @@ sh_can_multi_conn (void *handle)
return boolean_method (handle, "can_multi_conn");
}
+static int
+sh_can_cache (void *handle)
+{
+ return boolean_method (handle, "can_cache");
+}
+
static int
sh_flush (void *handle, uint32_t flags)
{
@@ -782,6 +788,38 @@ sh_extents (void *handle, uint32_t count, uint64_t offset, uint32_t
flags,
}
}
+static int
+sh_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
+{
+ char *h = handle;
+ char cbuf[32], obuf[32];
+ const char *args[] = { script, "cache", h, cbuf, obuf, NULL };
+
+ snprintf (cbuf, sizeof cbuf, "%" PRIu32, count);
+ snprintf (obuf, sizeof obuf, "%" PRIu64, offset);
+ assert (!flags);
+
+ switch (call (args)) {
+ case OK:
+ return 0;
+
+ case MISSING:
+ /* Ignore lack of cache callback. */
+ return 0;
+
+ case ERROR:
+ return -1;
+
+ case RET_FALSE:
+ nbdkit_error ("%s: %s method returned unexpected code (3/false)",
+ script, "cache");
+ errno = EIO;
+ return -1;
+
+ default: abort ();
+ }
+}
+
#define sh_config_help \
"script=<FILENAME> (required) The shell script to run.\n" \
"[other arguments may be used by the plugin that you load]"
@@ -812,6 +850,7 @@ static struct nbdkit_plugin plugin = {
.can_extents = sh_can_extents,
.can_fua = sh_can_fua,
.can_multi_conn = sh_can_multi_conn,
+ .can_cache = sh_can_cache,
.pread = sh_pread,
.pwrite = sh_pwrite,
@@ -819,6 +858,7 @@ static struct nbdkit_plugin plugin = {
.trim = sh_trim,
.zero = sh_zero,
.extents = sh_extents,
+ .cache = sh_cache,
.errno_is_preserved = 1,
};
--
2.20.1
3:01 a.m.
New subject: [nbdkit PATCH 6/9] sh: Implement .cache script callback
For this plugin, if a tri-state can_cache is implemented, the code
from sh_can_fua could be reused:
https://github.com/libguestfs/nbdkit/blob/7a4f38f98920a1192e5c50ea9bd212e...
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine. Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/
10:03 p.m.
New subject: [nbdkit PATCH 7/9] filters: Add .cache callback
Make it possible for filters to adjust the behavior for
NBD_CMD_CACHE. To avoid any 'git bisect' breakage, this patch defaults
.can_cache to false until all necessary filters have been patched
first.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
docs/nbdkit-filter.pod | 27 ++++++++++++++++++++++++++-
include/nbdkit-filter.h | 8 ++++++++
server/filters.c | 39 +++++++++++++++++++++++++++++++++------
3 files changed, 67 insertions(+), 7 deletions(-)
diff --git a/docs/nbdkit-filter.pod b/docs/nbdkit-filter.pod
index 6aeaa7b..787333a 100644
--- a/docs/nbdkit-filter.pod
+++ b/docs/nbdkit-filter.pod
@@ -356,6 +356,8 @@ calls.
=head2 C<.can_multi_conn>
+=head2 C<.can_cache>
+
int (*can_write) (struct nbdkit_next_ops *next_ops, void *nxdata,
void *handle);
int (*can_flush) (struct nbdkit_next_ops *next_ops, void *nxdata,
@@ -373,6 +375,8 @@ calls.
void *handle);
int (*can_multi_conn) (struct nbdkit_next_ops *next_ops, void *nxdata,
void *handle);
+ int (*can_cache) (struct nbdkit_next_ops *next_ops, void *nxdata,
+ void *handle);
These intercept the corresponding plugin methods, and control feature
bits advertised to the client.
@@ -597,6 +601,27 @@ Returns the number of extents in the list.
Returns a copy of the C<i>'th extent.
+=head2 C<.cache>
+
+ int (*cache) (struct nbdkit_next_ops *next_ops, void *nxdata,
+ void *handle, uint32_t count, uint64_t offset,
+ uint32_t flags, int *err);
+
+This intercepts the plugin C<.cache> method and can be used to modify
+cache requests.
+
+This function will not be called if C<.can_cache> returned false; in
+turn, the filter should not call C<next_ops-E<gt>cache> if
+C<next_ops-E<gt>can_cache> did not return true.
+
+The parameter C<flags> exists in case of future NBD protocol
+extensions; at this time, it will be 0 on input, and the filter should
+not pass any flags to C<next_ops-E<gt>cache>.
+
+If there is an error, C<.cache> should call C<nbdkit_error> with an
+error message B<and> return -1 with C<err> set to the positive errno
+value to return to the client.
+
=head1 ERROR HANDLING
If there is an error in the filter itself, the filter should call
@@ -708,4 +733,4 @@ Richard W.M. Jones
=head1 COPYRIGHT
-Copyright (C) 2013-2018 Red Hat Inc.
+Copyright (C) 2013-2019 Red Hat Inc.
diff --git a/include/nbdkit-filter.h b/include/nbdkit-filter.h
index 9b6cd6e..5893dd8 100644
--- a/include/nbdkit-filter.h
+++ b/include/nbdkit-filter.h
@@ -74,6 +74,7 @@ struct nbdkit_next_ops {
int (*can_extents) (void *nxdata);
int (*can_fua) (void *nxdata);
int (*can_multi_conn) (void *nxdata);
+ int (*can_cache) (void *nxdata);
int (*pread) (void *nxdata, void *buf, uint32_t count, uint64_t offset,
uint32_t flags, int *err);
@@ -87,6 +88,8 @@ struct nbdkit_next_ops {
int *err);
int (*extents) (void *nxdata, uint32_t count, uint64_t offset, uint32_t flags,
struct nbdkit_extents *extents, int *err);
+ int (*cache) (void *nxdata, uint32_t count, uint64_t offset, uint32_t flags,
+ int *err);
};
struct nbdkit_filter {
@@ -142,6 +145,8 @@ struct nbdkit_filter {
void *handle);
int (*can_multi_conn) (struct nbdkit_next_ops *next_ops, void *nxdata,
void *handle);
+ int (*can_cache) (struct nbdkit_next_ops *next_ops, void *nxdata,
+ void *handle);
int (*pread) (struct nbdkit_next_ops *next_ops, void *nxdata,
void *handle, void *buf, uint32_t count, uint64_t offset,
@@ -161,6 +166,9 @@ struct nbdkit_filter {
int (*extents) (struct nbdkit_next_ops *next_ops, void *nxdata,
void *handle, uint32_t count, uint64_t offset, uint32_t flags,
struct nbdkit_extents *extents, int *err);
+ int (*cache) (struct nbdkit_next_ops *next_ops, void *nxdata,
+ void *handle, uint32_t count, uint64_t offset, uint32_t flags,
+ int *err);
};
#define NBDKIT_REGISTER_FILTER(filter) \
diff --git a/server/filters.c b/server/filters.c
index c619fd6..a48f67e 100644
--- a/server/filters.c
+++ b/server/filters.c
@@ -329,6 +329,13 @@ next_can_multi_conn (void *nxdata)
return b_conn->b->can_multi_conn (b_conn->b, b_conn->conn);
}
+static int
+next_can_cache (void *nxdata)
+{
+ struct b_conn *b_conn = nxdata;
+ return b_conn->b->can_cache (b_conn->b, b_conn->conn);
+}
+
static int
next_pread (void *nxdata, void *buf, uint32_t count, uint64_t offset,
uint32_t flags, int *err)
@@ -379,6 +386,15 @@ next_extents (void *nxdata, uint32_t count, uint64_t offset, uint32_t
flags,
extents, err);
}
+static int
+next_cache (void *nxdata, uint32_t count, uint64_t offset,
+ uint32_t flags, int *err)
+{
+ struct b_conn *b_conn = nxdata;
+ return b_conn->b->cache (b_conn->b, b_conn->conn, count, offset, flags,
+ err);
+}
+
static struct nbdkit_next_ops next_ops = {
.get_size = next_get_size,
.can_write = next_can_write,
@@ -389,12 +405,14 @@ static struct nbdkit_next_ops next_ops = {
.can_extents = next_can_extents,
.can_fua = next_can_fua,
.can_multi_conn = next_can_multi_conn,
+ .can_cache = next_can_cache,
.pread = next_pread,
.pwrite = next_pwrite,
.flush = next_flush,
.trim = next_trim,
.zero = next_zero,
.extents = next_extents,
+ .cache = next_cache,
};
static int
@@ -577,12 +595,16 @@ static int
filter_can_cache (struct backend *b, struct connection *conn)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
+ void *handle = connection_get_handle (conn, f->backend.i);
+ struct b_conn nxdata = { .b = f->backend.next, .conn = conn };
debug ("%s: can_cache", f->name);
- /* FIXME: Default to f->backend.next->can_cache, once all filters
- have been audited */
- return 0;
+ if (f->filter.can_cache)
+ return f->filter.can_cache (&next_ops, &nxdata, handle);
+ else
+ return 0; /* FIXME - allow passthrough once all filters are audited */
+ return f->backend.next->can_cache (f->backend.next, conn);
}
static int
@@ -720,15 +742,20 @@ filter_cache (struct backend *b, struct connection *conn,
uint32_t flags, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
+ void *handle = connection_get_handle (conn, f->backend.i);
+ struct b_conn nxdata = { .b = f->backend.next, .conn = conn };
assert (flags == 0);
debug ("%s: cache count=%" PRIu32 " offset=%" PRIu64 "
flags=0x%" PRIx32,
f->name, count, offset, flags);
- /* FIXME: Allow filter to rewrite request */
- return f->backend.next->cache (f->backend.next, conn,
- count, offset, flags, err);
+ if (f->filter.cache)
+ return f->filter.cache (&next_ops, &nxdata, handle,
+ count, offset, flags, err);
+ else
+ return f->backend.next->cache (f->backend.next, conn,
+ count, offset, flags, err);
}
static struct backend filter_functions = {
--
2.20.1
10:03 p.m.
New subject: [nbdkit PATCH 8/9] test-layers: Test .cache usage
This also forms the first instance that I am aware of where an open
source client actually sends NBD_CMD_CACHE to the server - even if the
client is just a test app (the nbd plugin doesn't count - it won't
send to the server unless a client sends to the plugin first).
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
tests/test-layers-filter.c | 22 +++++++++++++++++++++-
tests/test-layers-plugin.c | 17 +++++++++++++++++
tests/test-layers.c | 36 ++++++++++++++++++++++++++++++++++++
3 files changed, 74 insertions(+), 1 deletion(-)
diff --git a/tests/test-layers-filter.c b/tests/test-layers-filter.c
index a8f4723..bd063bd 100644
--- a/tests/test-layers-filter.c
+++ b/tests/test-layers-filter.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2018 Red Hat Inc.
+ * Copyright (C) 2018-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -184,6 +184,15 @@ test_layers_filter_can_extents (struct nbdkit_next_ops *next_ops,
return next_ops->can_extents (nxdata);
}
+static int
+test_layers_filter_can_cache (struct nbdkit_next_ops *next_ops,
+ void *nxdata,
+ void *handle)
+{
+ DEBUG_FUNCTION;
+ return next_ops->can_cache (nxdata);
+}
+
static int
test_layers_filter_pread (struct nbdkit_next_ops *next_ops, void *nxdata,
void *handle, void *buf,
@@ -241,6 +250,15 @@ test_layers_filter_extents (struct nbdkit_next_ops *next_ops, void
*nxdata,
return next_ops->extents (nxdata, count, offset, flags, extents, err);
}
+static int
+test_layers_filter_cache (struct nbdkit_next_ops *next_ops, void *nxdata,
+ void *handle, uint32_t count, uint64_t offset,
+ uint32_t flags, int *err)
+{
+ DEBUG_FUNCTION;
+ return next_ops->cache (nxdata, count, offset, flags, err);
+}
+
static struct nbdkit_filter filter = {
.name = "testlayers" layer,
.version = PACKAGE_VERSION,
@@ -262,12 +280,14 @@ static struct nbdkit_filter filter = {
.can_fua = test_layers_filter_can_fua,
.can_multi_conn = test_layers_filter_can_multi_conn,
.can_extents = test_layers_filter_can_extents,
+ .can_cache = test_layers_filter_can_cache,
.pread = test_layers_filter_pread,
.pwrite = test_layers_filter_pwrite,
.flush = test_layers_filter_flush,
.trim = test_layers_filter_trim,
.zero = test_layers_filter_zero,
.extents = test_layers_filter_extents,
+ .cache = test_layers_filter_cache,
};
NBDKIT_REGISTER_FILTER(filter)
diff --git a/tests/test-layers-plugin.c b/tests/test-layers-plugin.c
index f9b2014..981641e 100644
--- a/tests/test-layers-plugin.c
+++ b/tests/test-layers-plugin.c
@@ -143,6 +143,13 @@ test_layers_plugin_can_multi_conn (void *handle)
return 1;
}
+static int
+test_layers_plugin_can_cache (void *handle)
+{
+ DEBUG_FUNCTION;
+ return 1;
+}
+
static int
test_layers_plugin_can_extents (void *handle)
{
@@ -201,6 +208,14 @@ test_layers_plugin_extents (void *handle,
return nbdkit_add_extent (extents, offset, count, 0);
}
+static int
+test_layers_plugin_cache (void *handle,
+ uint32_t count, uint64_t offset, uint32_t flags)
+{
+ DEBUG_FUNCTION;
+ return 0;
+}
+
static struct nbdkit_plugin plugin = {
.name = "testlayersplugin",
.version = PACKAGE_VERSION,
@@ -220,12 +235,14 @@ static struct nbdkit_plugin plugin = {
.can_fua = test_layers_plugin_can_fua,
.can_multi_conn = test_layers_plugin_can_multi_conn,
.can_extents = test_layers_plugin_can_extents,
+ .can_cache = test_layers_plugin_can_cache,
.pread = test_layers_plugin_pread,
.pwrite = test_layers_plugin_pwrite,
.flush = test_layers_plugin_flush,
.trim = test_layers_plugin_trim,
.zero = test_layers_plugin_zero,
.extents = test_layers_plugin_extents,
+ .cache = test_layers_plugin_cache,
/* In this plugin, errno is preserved properly along error return
* paths from failed system calls.
*/
diff --git a/tests/test-layers.c b/tests/test-layers.c
index 627e4ec..a820ba5 100644
--- a/tests/test-layers.c
+++ b/tests/test-layers.c
@@ -361,6 +361,12 @@ main (int argc, char *argv[])
"filter1: test_layers_filter_can_extents",
"test_layers_plugin_can_extents",
NULL);
+ log_verify_seen_in_order
+ ("filter3: test_layers_filter_can_cache",
+ "filter2: test_layers_filter_can_cache",
+ "filter1: test_layers_filter_can_cache",
+ "test_layers_plugin_can_cache",
+ NULL);
fprintf (stderr, "%s: protocol connected\n", program_name);
@@ -526,6 +532,36 @@ main (int argc, char *argv[])
"test_layers_plugin_zero",
NULL);
+ request.type = htobe16 (NBD_CMD_CACHE);
+ request.offset = htobe64 (0);
+ request.count = htobe32 (512);
+ request.flags = htobe16 (0);
+ if (send (sock, &request, sizeof request, 0) != sizeof request) {
+ perror ("send: NBD_CMD_CACHE");
+ exit (EXIT_FAILURE);
+ }
+ if (recv (sock, &reply, sizeof reply, MSG_WAITALL) != sizeof reply) {
+ perror ("recv: NBD_CMD_CACHE");
+ exit (EXIT_FAILURE);
+ }
+ if (reply.error != NBD_SUCCESS) {
+ fprintf (stderr, "%s: NBD_CMD_CACHE failed with %d\n",
+ program_name, reply.error);
+ exit (EXIT_FAILURE);
+ }
+
+ sleep (1);
+ log_verify_seen_in_order
+ ("testlayersfilter3: cache count=512 offset=0 flags=0x0",
+ "filter3: test_layers_filter_cache",
+ "testlayersfilter2: cache count=512 offset=0 flags=0x0",
+ "filter2: test_layers_filter_cache",
+ "testlayersfilter1: cache count=512 offset=0 flags=0x0",
+ "filter1: test_layers_filter_cache",
+ "testlayersplugin: debug: cache count=512 offset=0",
+ "test_layers_plugin_cache",
+ NULL);
+
/* XXX We should test NBD_CMD_BLOCK_STATUS here. However it
* requires that we negotiate structured replies and base:allocation
* in the handshake, and the format of the reply is more complex
--
2.20.1
10:03 p.m.
New subject: [nbdkit PATCH 9/9] blocksize: Implement .cache rounding
Rely on .can_cache passthrough to imply that our .cache won't be
called unless the plugin also has .cache. [Technically, that won't
happen until a later patch flips the default in filters.c]. Round the
cache request out, to cache the same range as would otherwise be
passed to the plugin's .pread if we had set .can_cache to
false. Fortunately, when maxlen is larger than maxblock, and the
plugin supports .cache, this results in a lot fewer calls into the
plugin than the .pread fallback.
Oddly enough, a client can submit an unaligned request for just under
4G of caching where our rounding would overflow a 32-bit integer, so
our rounding has to use a 64-bit temporary.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
filters/blocksize/blocksize.c | 31 ++++++++++++++++++++++++++++++-
1 file changed, 30 insertions(+), 1 deletion(-)
diff --git a/filters/blocksize/blocksize.c b/filters/blocksize/blocksize.c
index 4f3e9a3..2d28222 100644
--- a/filters/blocksize/blocksize.c
+++ b/filters/blocksize/blocksize.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2018 Red Hat Inc.
+ * Copyright (C) 2018-2019 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -389,6 +389,34 @@ blocksize_extents (struct nbdkit_next_ops *next_ops, void *nxdata,
flags, extents, err);
}
+static int
+blocksize_cache (struct nbdkit_next_ops *next_ops, void *nxdata,
+ void *handle, uint32_t count, uint64_t offs, uint32_t flags,
+ int *err)
+{
+ uint32_t limit;
+ uint64_t remaining = count; /* Rounding out could exceed 32 bits */
+
+ /* Unaligned head */
+ limit = offs & (minblock - 1);
+ remaining += limit;
+ offs -= limit;
+
+ /* Unaligned tail */
+ remaining = ROUND_UP (remaining, minblock);
+
+ /* Aligned body */
+ while (remaining) {
+ limit = MIN (maxdata, remaining);
+ if (next_ops->cache (nxdata, limit, offs, flags, err) == -1)
+ return -1;
+ offs += limit;
+ remaining -= limit;
+ }
+
+ return 0;
+}
+
static struct nbdkit_filter filter = {
.name = "blocksize",
.longname = "nbdkit blocksize filter",
@@ -404,6 +432,7 @@ static struct nbdkit_filter filter = {
.trim = blocksize_trim,
.zero = blocksize_zero,
.extents = blocksize_extents,
+ .cache = blocksize_cache,
};
NBDKIT_REGISTER_FILTER(filter)
--
2.20.1
2019
days inactive
2022
days old
12 comments
2 participants
participants (2)
-
Eric Blake -
Richard W.M. Jones